Polyurethane front control arm bushings. 3

[Mazda Carnage]

I am in the process of putting my 1988 Mazda 626GT in a new body.

Many things on the car are getting revamped.

The car has bolt on performance struts and 1" lowering springs, oversized sway bars and custom oversized poly link kits.
Strut tower bars, trailing axle bar, poly sway bar bushings. 4 new trailing axle arms, polyurethane trailing link bars, customized ball joint bolts...


I sandblasted 2 front control arms, pressed out the factory bushings, welded reinforcements for the link kit cups and welded steel loops for suspension travel limiting tie down straps for drag track use. Then installed 4 Nolathane polyurethane bushings.

The factory front control arm bushings are chemically bonded to the center sleeve, when the control arm is bolted to the crossmember at the ride height position (about 15degrees downward) the factory control arm bushings have a torsion resistance, it takes about 200 lbs pressure on old bushings to raise the control arm level with the crossmember so the factory front control arm bushings have a combined maximum resistance of 400-500 pounds. So if you remove the struts with springs the front control arm bushings will hold the front end of the car up and keep the crossmembers from hitting the ground.

The new Nolathane bushings use a greased center sleeve, the poly bushing is a bit longer than the center sleeve which would add some pressure to the center sleeve. But because it is greased at the center point the control arm will at some point move up or down on the center sleeve.
My concerns is that at the point the bushings move on the center sleeves, to the struts, springs and sway bar it would be as though the front end weight of the car has increased or the spring rate and swaybar size was lowered.

These are the bushings:

The Poly control arm bushings are meant to reduce torque steer by reducing control arm torsion under acceleration.
On my 1989 MX6 GT I used a bunch of old CV joint nuts that I ground down, put on both sides of the control arm bushings and pounded the control arms into the crossmembers. The nuts filled the gap between the control arm bushings rubber and crossmember, allowed up and down movement but 0 deflection, the car has no torque steer and rides great.
On the old 626GT the control arm bushings where a bit warn, I welded washers to the end of the control arm boxing in the bushing, the hole in the washer is the same size as the center sleeve and stops any torque deflection but allows up and down movement.
I ordered Polyurethane control arm bushings for both cars a few years back thinking it would stiffen up and down travel of the control arm and have 0 torque steer like both my cheap solutions to torque steer.
Now I am worried these Poly bushings might do the opposite of what I bought them for.


I contacted Nolathane with these concerns when I received the bushings years ago and also asked what boding agent they use to adhere the polyurethane to the outer sleeve but they did not reply.
I cannot find the polyurethane durometer rating but I would say they are high 70's-low 80's.

I told myself to quit worrying about this before I started assembling and welding the front control arms, after about 40hours work so far on the control arms and crossmembers and front sub frame getting them all to bare metal and ready to paint with POR15 and top coat, I still have to press in new ball joints and tack weld them, the Por15 cost 88$, the ball joints another 50$. Por15 is a pain in the ass to use, after bringing the part to bare metal it must be washed in expensive marine clean degreaser, rinsed, dried, sprayed with metal ready etching acid, rinsed, dried then painted.
My though was to try them with grease and if they suck try to clean them and bond the center sleeve in place, but that would be a pain and I'm not sure what Nolathane's "special squeak free grease" is made or of if it penetrates/conditions the polyurethane, can it be cleaned off 100%.

Before I go any farther with these control arms I really want another opinion.
Are my concerns about this design justified or ridiculous?
From my searching I have found similar (Not my make or model) polyurethane bushings with chemically bonded outer and inner sleeves. At what durometer would this be feasible and what bonding agent would be best for poly to mild steel?
I have many more control arms, 4moog double sleeved factory front control arm bushings would be about 120$, this time I would use the welded washer method (one at the front of the control arm and one at the back of the arm) then press in the bushings, this would allow the control arm to only move up and down and give more up and down resistance than worn out factory bushings but require a lot of work again and more money.

I live in Quebec Canada the roads are riddled with pot hole, ruts from heavy trucks during winter thaw and speed bumps. The cars weighs about 2650lbs, has 450 ft-lb instant wheel torque and is front wheel drive.
With all the work on the new body the only thing I am not working on is producing more power, I am adding piggy timing control over factory (modified) and better control over fuel, 3 stages of boost control (was 2) and 3 water meth stages (was two), everything else is handling, durability, braking and acceleration control.
This was a no budget build and managed 30psi boost on factory timing thanks to water/methanol injection, the MX6 has a laundry list of better performance parts on it and ready to install and is meant to be faster than the 626GT but the 626GT turned out to be faster than I expected any of my cars to be, never thought I would say this but it is fast enough.


Suggestions?

 

[BrianPetersen]

If you plan to drive the car in winter and use it as a daily driver on those rough roads and put a lot of kilometers on it, I'd recommend stock bushings or equivalent (with bonded rubber and no sliding surfaces). I have no idea what durometer is required for bonded bushings to become viable, but it has to be pretty soft and compliant and accommodate a lot of deflection for that solution to work.

If it's only going to see racetrack use and only in summer and not accumulate a lot of mileage, you could use either one.

The issue with the sliding polyurethane bushes is that dirt and grime (and corrosion) will get in there and wear them out. This doesn't happen with the bonded type. This is why the auto industry switched to the bonded bushings sometime in the 1970s. Maintenance free. No more suspension grease jobs.

The issue with high-durometer polyurethane in those applications is that the amount of NVH transmitted straight through into the bodyshell will rattle your teeth out.

I have no idea how this would have anything to do with torque steer. The sloppiness that will surely accumulate after the bushes have worn their own clearance due to dirt and dust and water intrusion would surely be worse in the long term, no?

 

[Mazda Carnage]

I agree, but in some cases to get the handling polyurethane offers over rubber a free sliding design is required (not in the case of my control arms), some companies bond Teflon to the inside of the bushing so it never requires lubrication.

Short response:
-All my modified cars are daily drivers (life is too short).
-I have no concerns about about dirt, water or debris getting into the bushings because of their fitment.
-I have no concerns with NVH from these bushings because of the no budget metal to metal solutions I have used in the past have no issues.
-Deflection and play in front end components on front wheel drive cars effect wheel toe and camber which causes torque steer and can cause open differential to move power between the wheels (really long thin axle can also cause this)= Front wheel drive Torque steer.
-My concern is what happens when a solid part that offers suspension resistance at a certain point is allowed to slide freely.

Long explanation:
I am just guessing the Durometer, I have 2 polyurethane 3 foot long bars, the first one was a website online order mistake, the default bar was 3feet X 2in black 60 durometer, then you select color and durometer and place the order, no mater what you would select or it showed in the shopping cart they got an order for black 60. they acknowledged it was a programming problem and billed me another 320$ and shipped the correct bar red durometer 97.

97 Durometer shore A is rock hard, I have 3 sets of 97 durometer motor mounts for these cars and drilled 1/8" relief holes around the mounts to reduce the engine vibrations through the cars. Every bolt and nut gets locktite.

60 Durometer is very soft, it cant be machined and can barely be worked with, it is softer than any factory bushing, it's to soft and squishy to use as compressor vibration pucks...

The Poly Control arm bushings are much softer than poly motor mounts or sway bar bushings.
According to Nolathane less than 1% of their bushings are 93 duro and above the rest are 74 or 85 duro.
Because I don't have a durometer gauge and haven't worked with 74 or 85 durometer before it's hard to tell I would guess 74 but could be wrong.

Moog factory replacement bushings are pretty stiff.

I have a new moog bushing that seems as stiff as the poly bushings, the factory bushings and the moog bushings have a much thicker center sleeve and outer casing so a smaller rubber area. Some of the factory or replacement aftermarket bushings have hollow spots in the rubber, I know the moogs are solid rubber. But the moog control arms alone are not enough to stop torque steer on these cars. The Moog control arms and other aftermarket control arm are made of thinner metal than the factory 1988 control arm, the sway bars and link kits I run rip the link kit cup from the control arms if I weld in the cup then it rips a big chunk out of the control arm. After installing the aftermarket sway bars and supplied link kits it didn't take long before the roads here snapped the link kit bolt and all the poly bushings "and lifetime warranty" went away. I drilled out the link kit bushings and washer cups, used 1/2" diameter bolts and sections of a small floor jack bar as sleeves, this exposed the next weakest link : the control arms.

Ball joints had a similar problem with the local roads and would cause cupping in the spindle from the base of the ball joint shaft, this would eventually cause play even with new ball joints and would kill ball joints faster. the Ball joint is held in place with an M8 bolt that meets a groove in the ball joint shaft. I found that drilling out the spindle and using an M12 grade 10.9 bolts and extra torque prevented all wear, cupping and play from starting. This created a different problem because the pothole and road bump energy wanted to go somewhere, the ball joint is pressed into the control arm and aftermarket control arms with pressed in ball joints would drop down and out of the control arm. Ball joints with a retaining clip was thought to be the solution but resulted in cupping the control arm until the ball joint floated around in the control arm or ripped out. This happened mostly the my shop partner who drove the same cars but less modified he lived way out in the country where the roads where even worse and he always though it easier to buy a complete control arm than swap a ball joint one of the many control arms we accumulated over years of parting these model cars. He was wrong.

The final solution was to use a press in ball joint with retaining clip and grease fitting, fill it with high temp water proof grease, keep it cool, tack weld it to the control arm in three place at the bottom, and use the M12 retaining bolt.
Keep the ball joint greased, face pot holes head on and the ball joints never seem to fail.



I use a 5 foot long 12lbs wrecking bar to pry between the control arm and crossmember if there is any deflection (outer sleeve/control arm moves towards the center sleeve) it will result in torque steer. If the control arm deflects backward under acceleration it moves the pall joint back toward the firewall and in towards the wheel well. 1MM deflection at the control arm is a lot more at the ball joint, moving the ball joint effects the toe and camber of the wheel.
When launching or doing burnouts with an opened differential this can cause just one wheel to spin or the differential to send power back and forth from wheel to wheel.
Perhaps if all things where equal same controls arms in the same condition and the car had a limited slip differential and both control arms deflected equally the car would stay straight. But when passing a logging truck on a rutty road this could still create issues.

I am hoping the fact that the Polyurethane i in the Nolathan bushings is longer than the center sleeve and crossmember box will leave it no room for deflection.

This is the crossmember set-up:

A bad drawing.
I have read about wear/cupping and abrasion of poly bushings with free floating components.

But in this case both ends of every poly control arm busing is boxed in by the cross member, it's a bad drawing but they are completely covered, because the bushing center sleeve is exactly the length of the crossmember opening and the bushing is longer it will be crushed into the crossmember box making it very hard for any dirt to get in between the crossmember metal and poly bushing ends and even harder to get between the center sleeve and bushing.

As for NVH I don't think under regular circumstances there would be much difference between a chemically bonded poly bushing and sleeve and a pressure bonded bushing and sleeve, the sleeve is bigger than the bushing center hole it needs to be lubricated to press it in, I doubt I could press one in dry for testing purposes and if I did I probably couldn't press it out, between that and the poly being crushed at both ends by the crossmember there will be some resistance before the bushing articulates on the center sleeve.
My fear is what happens when it does articulate, say a lightly banked right corner at 112mph under acceleration and as the cars weight shifts from the right front wheel to the left after the apex the control arms decide to articulate right down and left up and the car wanders to the left.
Or going over a large speed bump where both sides of the front end move together so the giant sway bar articulates in it's rock hard bushings and the giant link kits do nothing to hold up the front end and the cars moving slow so there is no sudden travel for the struts to react to, the front end dips on the coil springs and control arm bushings then the control arm bushings articulate and? Never have I bottomed one of these cars out, I don't even run bump stops on any of my struts, never had to.
My garages old location was next to a never used industrial road, the road was brutal. My friends and I and the other shop owners and their friends all raced on this road, I can't count the number of cars that bottomed out and cracked their oil pans, I never worried because the cross members sit lower than the oil pan and go all the way to the front making it impossible for the pan to hit the grown on a flat surface but the crossmembers never bottomed out, the cars handled all the dips and potholes under heavy acceleration in a straight line.


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New question:
If a bushing that binds but at some point can travel freely and offer 0rsistance is used to replace a bushing that offered enough resistance to hold up a car and could not travel freely but instead bind and offer more resistance the more it travels. Is that bushing crap without changing strut and spring rates accordingly.

If the answer is, I am not changing suspension set-ups.
Therefore I have nothing to loose trying.
So does anyone know a good chemical bonding agent (glue/adhesive) to bond polyurethane to steel ?

 

[cibachrome]

If you want exceptional handling, that comes from an exceptional set of tires. Bushings only contribute 10-15% to the 'handling' of a vehicle in case you didn'y know that(or even less, it depends on the suspension type). You will still have kinematic compliance and but a reduced deflection contribution. Wooppee do. Plus, if the kinematic component isn't reduced, you will probably BREAK some of the bushing attachments and fasteners because most suspensions are over-constrained. If you like driving on a straight road while eating with both hands, the nylon jobs will certainly help.

You didn't mention the steering gear (or maybe you did but I missed it in the windage). Solid mount that baby and you will crack the gear housing. A common foible.

 

[BrianPetersen]

Well, the bushings will "contribute" when worn out ... A Ford van with Twin-I-Beam suspension with worn-out bushings goes whichever direction it wants to when there is a cross-wind, with the steering being merely a general suggestion.

 

[cibachrome]

OK, so I pawed thru my database and come up with 15 Mazda vehicles CX6,CX9, MX, RX, Miata, 3S, Tribute, etc looking for a Mazda 'recipe'.

Everything is 3-5% front roll steer, 0 - 4% rear roll steer, a bunch of front lateral force steer, same for rear (and of BOTH signs), and lots of front aligning moment steer that's flat with their Fy deflection steer counterparts. So it's not caster induced. Either a soft gear mount, power booster (valve of pump flow rate) or steering column.

That's where I'd put my money (besides oversized Summer tires and some larger, stiff, and wider wheels). BUT, the car will be a tad twitchy because it will have lost a bunch of understeer meaning the steering gain will be quite high if you exceed the speed limit by a factor of large values of 2.

 

[NormPeterson]

But in this case both ends of every poly control arm busing is boxed in by the cross member, it's a bad drawing but they are completely covered, because the bushing center sleeve is exactly the length of the crossmember opening and the bushing is longer it will be crushed into the crossmember box making it very hard for any dirt to get in between the crossmember metal and poly bushing ends and even harder to get between the center sleeve and bushing.

What you're doing there is bad on two accounts. First, you're exaggerating the amount of over-constraint, which the chassis brackets don't particularly like when there's any off-axis rotation, or when pairs of chassis-side sleeve axes are parallel but not concentric.

And second, you're basically "wasting" some of the fastener installation torque ending up with less clamping load through the sleeve, making it more likely to slip around in the bolt to hole clearances as the suspension moves under load.

The new Nolathane bushings use a greased center sleeve, the poly bushing is a bit longer than the center sleeve which would add some pressure to the center sleeve. But because it is greased at the center point the control arm will at some point move up or down on the center sleeve.
My concerns is that at the point the bushings move on the center sleeves, to the struts, springs and sway bar it would be as though the front end weight of the car has increased or the spring rate and swaybar size was lowered.

For the suspension to actually function, that's what you want. Polyurethane is far too rigid to allow much suspension movement via compliance. Yes, the effective wheel rate would be reduced, but that may not be a bad thing (think reduced variance in wheel loading over any given amount of suspension movement, which can't be completely eliminated).

Some of the factory or replacement aftermarket bushings have hollow spots in the rubber, I know the moogs are solid rubber. But the moog control arms alone are not enough to stop torque steer on these cars.

This is what is known as "voided bushing" technology, where somewhat more compliance in some loading directions is introduced without softening the directions you want kept firmer too much.

I'm thinking that it's lateral compliance at the control arm bushings that you're trying to minimize rather than vertical compliance at those locations or torsion in the control arms themselves.



Norm

 

[GregLocock]

In a typical L arm lower arm (ie an asymmetric wishbone) the usual setup is to have a stiff bush in line with the wheel centre, and a soft (NVH) bush on the long arm. This gives a degree of longitudinal compliance at the wheel, while allowing the lateral compliance to be low, in parallel with the tie rod. The vertical rates of those bushes can be softer or harder than the lateral rates, depending on all sorts of things.

In that design there is no benefit in stiffening the NVH bush, and the chances are the stiff bush is already stiffer than the subframe at that point.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[NormPeterson]

Greg - OP is specifically talking about a fairly serious drag racing situation where the traction load should be generating somewhat larger lateral loads on the NVH bushing than would be experienced in the car's original purpose as a street-driven entry-level to mid-level family sedan. I suspect if the lateral bushing was changed to polyurethane and the NVH bushing left as OE that the excess movement permitted by the NVH bushing would cause the polyurethane lateral bushing to fail after only a short time in this particular service.


Norm

 

[GregLocock]

Yup, good point.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[Mazda Carnage]

Thank you all for your replies.

If you want exceptional handling, that comes from an exceptional set of tires.

I wouldn't say I want exceptional handling as much as I want safe and reliable handling. I run sticky summer tires always have, no mater how good the tires are all I ever remember about them is how quickly they wore away. The tires that lasted me the longest (therefor those I rate as the best) where Falken FK451, they lasted me 1 full season, unfortunately they are discontinued.

What you're doing there is bad on two accounts. First, you're exaggerating the amount of over-constraint, which the chassis brackets don't particularly like when there's any off-axis rotation, or when pairs of chassis-side sleeve axes are parallel but not concentric.

And second, you're basically "wasting" some of the fastener installation torque ending up with less clamping load through the sleeve, making it more likely to slip around in the bolt to hole clearances as the suspension moves under load.

I didn't design the Nolathane bushings, that's the way they they came and are meant to be installed.
Again this isn't rock hard Polyurethane.

I doubt the sleeve will slip when bolted to the cross member.

Back to my no budget solutions.
On the 89MX6 GT I wanted to eliminate all lateral movement and seriously stiffen vertical travel.
I took 8 axle nuts, ground the collars down and rounded the nut a bit, I put 1 on each side of each control arm bushing, the control arm bushing and nuts where almost 3/4" wider than the crossmember boxes, I angled the nuts so that the edge of the lip and bushing sat in the crossmember box then I used a chain fall, huge ratchet straps and a sledge hammer to pull/pound the control arm into the crossmember. I tightened the retaining bolts (M12 grade 12.9) until the clamping force on the center sleeve was as great or greater than without the nuts.
The base of the nuts filled the gap between the crossmember and control arm eliminating all lateral movement of the control arm. The nut part I ground down got pressed into the bushing rubber on both sides compressing the rubber inside the bushing and greatly increasing the vertical resistance of the control arm. If before it took 200 lbs pressure to lower the control arm enough to pull the ball joint stem out of the spindle now it took over 350lbs pressure to lower the control arm that amount.
After installing the nuts the handling was perfect, no torque steer very little front end bouncing, didn't dip the front end in hard corners at full throttle and didn't increase road noise or vibrations at all, if it did the poly motor mounts drowns it out .

This video was after I installed the axle nuts in the crossmembers, the car is running 21psi boost on a T3 45trim turbo(Now 26 psi on T3stage3 T4 76trim):
Link

This is on Vernan Road and was filmed in 2005, after the last few winters of constant freezing and thawing all the roads here are as bad or worse than this road was. Vernan road today is way worse than it was then.

Both front wheels pull evenly, this car has manual rack and pinion and I blame the right dip in the burnout on my driving with one hand on the wheel for the first few seconds, not torque steer.

Another Video on the same set up and road :
Link

On the 1988 626GT runs another set of the same suspension parts, I welded washes to the control arm ends with holes in them the same size and the center sleeve, this eliminated all lateral movement, surprisingly there was no knocking or tapping between the washer and center sleeve. But did nothing for vertical movement and the 626GT does not handle as well as the MX6 when cornering because of this. It handles like my 1988 mx6GT does and the 89 Mx6 gt did before I installed the washers.
In the video's you will notice an S curve, near the top of the right hand turn there is a bump in the road, with both MX6's I ended up facing the wound in that corner, the car would bounce and lift enough weight off the front wheels, that for a fraction of a second I over turn the steering wheel (manual rack) I correct but the weight of the car comes down on the front left wheel the car dips and and the rear end tries to pass the front .

Installing the axle nuts in the control arms helped keep the weigh on the front wheels, but you will notice in both videos I am cautious with dips and bumps in those corners, after a couple years of testing the cars handling and limits I was ripping through those corners without any worries thanks to the increased resistance in vertical travel of the control arm bushings packed with nuts.

The 626GT currently has the same front end dip and bounce problem and it is running water/methanol, 30psi on a 60% larger turbo than the MX6 gt was running in the videos. I was hoping that all new rear end trailing axle components, better front control arm bushings would reduce/eliminate this.
I feel like these bushings used with greased sleeves will make the dip and bounce problem worse.

I'm thinking that it's lateral compliance at the control arm bushings that you're trying to minimize rather than vertical compliance at those locations or torsion in the control arms themselves.

Ideally I would like to eliminate lateral travel and distortion in the control arm and double the vertical travel resistance of the factory control arm.

It's a safety and handling thing:
Road called Mountain Road, speed limit 90 km/h I'm coasting through a corner at 90km/h in the 89mx6 (before the control arm mod) breaking in the stage 4 clutch and I go over one of these rogue dips in the road, the front end bounce into the oncoming traffic lane, the drivers side outer tie rod nut stripped down to the cotter pin and the link kit ripped a chunk out of the control arm. Lager tie rod Nut with the same thread size and pith, a retaining nut and larger cotter pin prevented the tie rod nuts from ever stripping, all control arms got welded from that day on but the only thing that prevented that kind of dipping and body roll was stuffing the axle nuts in the control arms.

In 2009 with the 1989 MX6 GT (modified control arms) I was showing off to some coworkers (friends) leaving a building and floored it through a corner only to be surprised by the fact their is a speed bump in the apex of the corner (to keep idiots like me from doing what I was doing), I looked at the sidewalk and field thinking that where I'm ending up but the car did not bounce the weight of the car stayed on wheels and the car accelerated through the corner like there was no speed bump.
My 1988 mx6 and 626 would have both been in the field.

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So instead of scrapping the control arms and 2 sets of poly bushings, I'm thinking bond the center sleeve and see.
If it's to stiff drill 6, 1/8" thick holes in the around the center through the polyurethane from one end to the other.
If it's still to stiff try 1/4" holes,

 

[NormPeterson]

I didn't design the Nolathane bushings, that's the way they they came and are meant to be installed.

That may be the way Nola and the rest designed their bushings, but that doesn't make it a good design overall for the application.

In any event, wheel rates are best attended to via the suspension's springs and sta-bars, not the control arm bushings. With OE rubber bushings, some added wheel rate is unavoidable, but the whole point of allowing slip between the sleeve and the poly is to avoid the poly adding any wheel rate lest it fail (and likely rather quickly at that). Load follows the stiffness here . . .

I doubt the sleeve will slip when bolted to the cross member.

Any clamp load lost to compressing the polyurethane means that the sleeve will not be as tightly clamped, and less tightly clamped means that it will slip at a lower load than intended. How much less is anybody's guess, but in other cases where the OE rubber bushings were swapped out for polyurethane replacements this absolutely does happen, and fairly commonly at that. You can't count on the compressed poly for much help, because as soon as suspension movement forces it to rotate inside the bracket you've already got some rotational slippage going on, so adding a little translational slip to that would come easily.


Lastly, there's the matter of driving to existing road conditions and not letting yourself get out past what your skill set can support (very preferably with some margin on your abilities remaining). Coping with bumps and dips in the road while at or near full power is on you (just knowing where they are would be a start). But honestly? Save your hard driving for the track.


Norm